The invention relates to a pressure-medium-operated control device, specifically a hydraulic control device, in particular for controlling a transmission of a motor vehicle.
A hydraulic control device of this kind has a valve piston in a housing to set the shift levels of the transmission The valve piston Is arranged to slide axially in a bore hole of the,housing, and the shift levels of the transmission are determined by setting the axial position of the valve piston. A control device of this kind has become known from DE 198 26 747 which is hereby included by reference as additional background of the present application
Sliding valve pistons of the aforementioned kind can be operable manually, or they can be automated to set and hold the transmission at the desired shift level. For example, a transmission may be shiftable between the shift levels D, R, N and P, but the selection could also include additional settings. The letter D stands for xe2x80x9cforward Drive with automatic gear selectionxe2x80x9d, R stands for xe2x80x9cReversexe2x80x9d, N stands for xe2x80x9cNeutralxe2x80x9d (where the torque flow between the engine and the transmission output shaft is interrupted), and P stands for xe2x80x9cParkxe2x80x9d, i.e., the shift level where the transmission output is locked.
In motor vehicles with transmissions that have a hydraulic control device of the aforementioned kind, the components of the vehicle are individually separate until they become connected in the assembly process. In the assembly step where the control device with the valve piston is installed on the transmission housing or at another place in the motor vehicle, it is possible for the valve piston to become dislodged from its correct, preset position, so that the actuator element for the valve piston cannot be connected correctly to the valve piston in the assembly process. The special steps required to achieve a correct connection between the valve piston and the actuator in this case will add to the cost and complexity of the assembly process.
The dislodgement of the valve piston from its correct position during transport can be caused, e.g., by vibrations or by holding the control device in a non-horizontal position.
It is therefore the object of the present invention, to provide a control device that allows a sound installation and will function reliably after it has been installed.
Furthermore, these improvements of the control device are to be achieved in an uncomplicated and cost-effective manner.
In a hydraulic control device according to the invention, the foregoing objective is met by an arrangement where, prior to installing the control device housing on the transmission housing or on another component of the vehicle, the axial position of the valve piston in the control device housing is retained by a safety element, and where the retaining function of the safety element is automatically canceled as a result of the installation.
It is advantageous if the safety element is a swivel lever which on a first lever arm, has a fork that is engaged by a projection or collar of the valve piston. This engagement allows the valve piston to be secured in its axial position. In another embodiment, it is practical if the lever arm has a nose or finger that enters into a recess in the surface of the valve piston or between two raised collars of the valve piston and thereby secures the axial position of the valve piston.
According to a further concept within the scope of the invention, it is advantageous if the swivel lever has a second lever arm which, in the process of installing the control device on the transmission housing or on another component of the vehicle, is pushed or moved out of position, whereby the first lever arm with the fork or finger is removed from engagement, so that the valve piston is set free to move in the axial direction.
It is practical to configure the safety element in the form of a two-armed lever. In another embodiment, it is practical if,the lever is a one-armed lever.
It is particularly advantageous, if the safety element is configured as a two-armed lever, where the second lever arm is connected to a spring element that biases the fork or the finger of the first lever arm against the valve piston.
It is further practical, if the spring element is connected to the housing of the control device, e.g., by one or more screws.
It is particularly advantageous if the lever and the spring element are configured as a single integral component. In another embodiment, the lever and the spring element are designed as two components.
According to a further concept of the invention, it is practical if the safety element, such as a lever with or without spring element, is designed as a sheet metal part produced, e.g., by punching and bending. This will make the part particularly simple to manufacture. It is further practical if the safety element, such as a lever with or without spring element, is made of spring steel.
It is further practical if, in comparison to each other, the lever is designed to be inflexible with respect to bending while the spring is designed to be resiliently flexible.
It is particularly advantageous if the lever is swivelably mounted on or by means of a ridge of the housing of the control device. To allow the lever to be more securely positioned, the ridge can have a slot or groove in which the lever is supported. It can be advantageous if the slot or groove is formed in the casting of the housing of the control device or machined after the casting process, e.g., by milling or drilling.
It is advantageous, if the secured condition of the valve piston is automatically released as a result of connecting the control device to the transmission.
In accordance with a further concept of the invention, it is advantageous if the spring element and a holder element of a further component of the control device or the transmission are formed together as one integral unit.
In practice, the holder element that is connected or integrally formed with the spring element can be a retainer fork that engages and thereby axially secures a tube-shaped element. It is also advantageous if the retainer fork, the spring element and the lever are designed as one integral unit.
It is advantageous if the tube-shaped element is part of a hydraulic connection between the control device and a rotating part of the transmission, e.g., of a transmission shaft.
The novel features that are considered as characteristic of the invention are set forth in particular in the appended claims. The improved apparatus itself, however, both as to its construction, and its mode of operation, together with additional features and advantages thereof, will be best understood upon perusal of the following detailed description of certain presently preferred specific embodiments with reference to the accompanying drawing.